(1) Field of the Invention
The invention relates to the formation of tapered or beveled contact via holes which provide good step coverage when the contact via holes are filled with metal. The tapered or beveled contact via holes are formed using a wet etch as a first etching step thereby avoiding the formation of a re-entrance profile at the entrance of the contact via hole.
(2) Description of Related Art
High density integrated circuit technology requires the use of an insulating layer separating layers of metal electrode patterns formed over a semiconductor substrate containing device elements. Contact via holes must be formed in the insulating layer to form electrical connection to the contact areas in the semiconductor substrate. These contact via holes require good metal stepcoverage to insure reliable electrical contacts with low contact resistance. For high density circuits good metal stepcoverage requires a contact via hole opening with a bevel or taper.
The importance of beveled contact holes has been recognized for some time and many have worked on methods of achieving them. U.S. Pat. No. 5,180,689 to Liu et al shows the formation of tapered contact via holes by a combination of anisotropic and isotropic etch steps. Using a dry etching step as a first step in the formation of tapered contact via holes has the problem of the formation of a re-entrance profile due to redepositing etched material at the entrance of the contact via hole. We have fabricated tapered contact via holes using a dry etching step as the first step with results as shown in FIG. 1. Etched material is redeposited at the entrance to the contact via hole 50 forming a re-entrance profile 52 and making the angle of entrance 54 into the contact via hole greater than 90.degree.. This makes it difficult to obtain good metal step coverage when the contact via hole is filled with metal. The current invention uses a wet etching step with a greater lateral etch rate than vertical etch rate as a first step in forming the tapered contact via hole. The wet etching prevents the formation of the re-entrance profile and provides an angle of entrance into the contact via hole of less than 90.degree..
U.S. Pat. No. 5,203,957 to Yoo et al uses argon sputter etching in the formation of contact via hole openings.